1 42 AGE, GROWTH, AND DEATH 



the one of the malarial parasite which I showed you a 

 few moments ago. The next slide, Fig. 51, exhibits an 

 organism which swims free in the water, and is pretty 

 well shown in this figure. It is called the Stentor, 

 Fig. 51, A. Here the chain of beads represents the 

 nucleus. The peculiar shape of the nucleus is a con- 

 stant characteristic of this animal. Upon the surface 

 of the body there are fine lines indicating superficial 

 structure. At the top there occurs what we call 

 the mouth. Over the rest of this minute organism 

 there is a thin cuticle, but at the mouth the cuticle is 

 absent, and the protoplasm is naked or uncovered so 

 that food can be taken in. There are bands of hairs 

 showing coarse and stiff in the figure but capable of 

 movement, and with the aid of its vibratile hairs, or 

 cilia, the organism can swim about in water. There is 

 another internal structure, the vacuole, shown in the 

 upper part of A as a circle. Obviously in an animal 

 Like this we no longer have simple protoplasm alone, 

 but protoplasm in part changed into other things. 

 Here then within the territory of a single cell we have 

 differentiation. If now in these unicellular organisms 

 we study both the protoplasm and the nucleus, we 

 learn that most of these modifications which are so 

 conspicuous upon microscopic observation are due to 

 changes in the protoplasm. It is the protoplasm 

 which acquires a new structure. In the resting nu- 

 cleus, on the contrary, we find perhaps a change of 

 form, minor details of arrangement by which one sort 

 of nucleus, or one stage of the nucleus, can be distin- 



